Magnetron



United States Patent MAGNETRON Myron S. Wheeler, Cedar Grove, N. J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 30, 1951, Serial No. 218,497

4 Claims. (Cl. 31539.63)

My invention relates broadly to ultra high frequency devices and more particularly to a method for frequency modulating a magnetron.

In the prior art magnetrons have been frequency modulated by changing the dielectric constant of the resonant circuit by either mechanical or electronic means.

The principal object of my invention is to provide an improved and simple method of frequency modulating a magnetron.

Another object of my invention is to frequency modulate a magnetron by electrical means.

Yet another object of my invention is to frequency modulate a magnetron by locally varying the intensity and distribution of the electric field between the cathode and anode.

A further object of my invention is to provide an electrode between the anode and the cathode of the magnetron to vary the intensity and distribution of the electric field between the anode and the cathode.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, together with additional objects and advantages thereof, may be best understood from the following description of the specific embodiment when read in conjunction with the accompanying drawing in which:

Figure 1 is an offset vertical cross-sectional view of a magnetron taken on line I-I of Fig. 2.

Figure 2 is a horizontal cross-sectional view, taken on line II-II of Fig. 1;

Figure 3 is a fragmentary section showing details of the electrode structure used with my invention;

Figure 4 is a fragmentary horizontal section showing details of a modified electrode structure.

A magnetron designated generally as 8 has a cylindrical anode structure 10 with an annular projection 12 which extends inwardly of the central part of the cylinder and which is provided with an axial cavity 14. End covers 16 and 18 close the upper and lower ends respectively of the cylindrical anode structure forming end spaces 20 and 22, respectively, between the end covers and the annular projection. Within the annular projection 12 and substantially coextensive therewith are cylindrical cavity resonators 24, each of which open in the end spaces 20 and 22 and whose axes are parallel to the axial cavity of the anode structure 10. The magnetron shown in the drawing has eight cavity resonators spaced equidistantly about the axial cavity 14. Each cavity of cavity resonators 24 opens into the axial cavity 14 through a capacitive radial slot 25 which is co-extensive with the length of the cavity resonator. Alternate separating partitions 26 between adjacent resonators 24 are tied together with conducting straps 27 and 28 which are recessed in the upper and lower horizontal faces 29 and 30 respectively of the annular projection 12. An elongated cathode 31 which projects into end spaces 20 and 22 and which is co-axial with the anode structure is mounted in the axial cavity 14 of the anode structure 2,765,424 Patented Oct. 2, 1956 10. Electrical connections to the cathode 31 are made through lead-in conductors 32 and 40 which are brought in through the body of cylindrical anode structure 10 into the end spaces 20 and 22, respectively. The faces of the annular projection 12 lying along the'axial cavity 14 and between the cavity resonators 24 constitute electron receiving portions, 33 of the anode structure 10. A means 42 to establish a magnetic field parallel to the axial cavity 14 is provided.

In operation, a difference of potential applied between the cathode and anode sets up a static electric field which, in the absence of other forces, tends to cause the electrons to travel from the cathode 31 to the anode 12. However, the interaction of the electric field and the magnetic field on the electrons causes the electrons to take a spiral path to the anode 12. Radio frequency fields are set up in the cavity resonators 24 and the electrons travelling from the cathode to the anode either delivery energy to or receive energy from these R. F. fields, a condition of oscillation being that the electrons deliver more energy to the R. F. field than they receive from the field. If an electron receives energy from the field, it is quickly sent back into the cathode 31 while those that deliver energy to the R. F. field continue on and eventually reach the anode 12. This selection and rejection of electrons causes a forming of spiral electron spokes in the interaction space between the anode and the cathode which rotate about the axis of the anode structure 10. .at an angular velocity which is a function of the magnetic field and the electric field.

The frequency of oscillation of the magnetron is largely determined by the inductance and the capacitance of the cavity resonators 24. However, the spiral spokes of electrons passing the radial slots 25 have an effect upon the oscillating frequency. It is this effect which I use to frequency modulate the tube. Generally speaking, the spokes must deliver energy to the R. F. oscillations at the same R. F. phase of each cycle. Consequently, if the angular velocity of the electrons is changed, the frequency of oscillation will also be changed in order to meet this condition. To vary the angular velocity and the speed of the electrons, I provide electrodes 34 which are set in the electron receiving portions 33 of the anode structure 10. The electrodes 34 are parallel to the cathode 31, extend the length of the annular projection 12 and into end space 22, and are connected together by a ring 36 which is located horizontally in the lower end space 22 of the magnetron. A lead-in conductor 38 runs from the ring 36 through the anode structure 10 to an outside source of modulating potential which is not shown. By applying a modulating potential to these electrodes 34, I may locally vary the electric field around each electrode, thereby varying the velocity of the electrons and the phase at which the radio frequency oscillations are reenforced by the spokes of electrons. In so doing, I also vary the frequency of the magnetron. Therefore by applying a modulating potential to the electrodes, I may frequency modulate the magnetron in accordance with the potential applied.

A modulating potential may be applied between the electrodes 34 and the anode 12 or between the electrodes and the cathode 31. In practice, I prefer to apply the potential between the electrode and the anode. For the maximum amount of frequency modulation, the potential applied to the electrode is swung both sides of the anode potential. However, if the modulating potential is driven positive with respect to the anode potential, the electrode will draw current. Therefore, it may be preferable to operate the electrode entirely below anode potential.

Figures 3 and 4 show the detailed construction of the electrode 34 which is set in recesses 35 in the electron receiving portion 33 of the anode structure 10 and insulated from the anode by, for instance, quartz-glass tubing 36. The electrode 34 in our particular structure is flush with the face of the electron receiving portions 33 of the anode structure. In Figure 3, the quartz insulator 36 is cut from a quartz-tube by splitting .thet'quart'zflube lengthwise along a chordal plane-,parallel to they axis of the tube. One side of the electrode: 34 isof cylindrical configuration having the same radius of curvature as the inside diameter of the quartz tube;

In Figure 4, the insulating quartz 3'6'is. ofi squared U-shaped cross section and correspondingly the electrode 34' is made of generally rectangular-cross-section.

An output loop 39 is provided to remove energy from the magnetron. The loop ishere sh'owntas brought. into one of the cavity resonators 24 throughthe w'all cylindrical anode structure 10:

It should be noted that while I' haveprovided: an' electrical means for frequency modulatinga magnetron, I have also provided a means which may be used to tune the magnetron. If a steady potential is applied to the electrode 34 instead of a varying potential, the? magnetron will operate at a frequency which is a function of the applied potential as well as of'the inductance and capacitance of the cavity resonators. Therefore,-the electrode 34 may also be used as a tuning means.

While I have shown and described a specific embodiment of our invention, I am fully aware that-many modifications thereof. are possible; I do not intend. to be restricted, therefore, except'as is necessitated by the prior art and by the spirit of my invention.

I claim:

1. An ultrahigh frequency device of the magnetron type comprising a cathode, an anode structure surrounding the cathode andhavingapluralityof'electron receiving portions with longitudinal recesses therein, cavity of. the) resonators connecting adjacent electron receiving portions, an electrode set into the recesses of and insulated from the electron receiving portions of the anode structure, means to apply a potential to said electrode.

2. An ultra high frequency device of the magnetron type comprising a cathode, an anode structure having a plurality of electron receiving portions with longitudinal recesses therein, cavity resonators connecting adjacent electron receiving portions, andelectrodes set into the recesses of and insulated from the electron receiving portions. a

3. An ultra high frequency device of the magnetron type comprising a cathode, an anode structure surrounding the cathode and having. a pluralityof'electron:receiving portions with longitudinal recesses therein, cavity resonators connecting adjacent electron receiving portions, an electrode set into each of said recesses and insulated from said electron receiving portions, and means to apply a potential to said electrodes.

4. An ultra high frequency device of the magnetron References Cited in the file of this patent UNITED STATES PATENTS 2,408,903 Biggs et a1. Oct. 8, 1946 2,412,772 Hansell Dec. 17, 1946 2,504,739 Shoupp Apr. 18, 1950 

